1. Field of the Invention
The present invention relates to an actuator where a solenoid valve is assembled and a solenoid valve control apparatus that controls a solenoid valve.
2. Description of the Related Art
It has heretofore been known a brake apparatus that applies a braking force by generating hydraulic pressure corresponding to an operation force of a brake pedal in a hydraulic circuit and supplying the hydraulic pressure to a wheel cylinder of each wheel (for example, see Patent Document 1). Between a hydraulic pressure source and each wheel cylinder, there are provided various solenoid valves, such as a pressure-increasing valve that is opened at the time of the supply of the hydraulic pressure, a pressure-decreasing valve that is opened at the time of the opening of the hydraulic pressure, and a switching valve that opens and closes at the time of the switching of a supply path of the hydraulic pressure. The brake apparatus adjusts the amount of a brake fluid to be supplied to the wheel cylinders by performing the opening/closing control of these solenoid valves, and applies an appropriate braking force to each wheel by controlling the hydraulic pressure.
In general, this kind of brake apparatus is formed in the form where most of solenoid valves and the hydraulic circuit are unitized as brake actuators. This actuator is formed by airtightly assembling a housing (where a hydraulic pressure passage is formed and bodies of a plurality of solenoid valves are assembled) with a terminal box (which covers and protects solenoids of the solenoid valves exposed from the housing). A circuit board on which a drive circuit for solenoids is mounted is housed in the terminal box. However, there is also a brake apparatus where an electronic control apparatus (hereinafter, referred to as an “ECU”) for controlling the actuators is housed in the terminal box for the purpose of the reduction of the size of the entire brake apparatus.    [Patent Document 1] Japanese Patent Application Publication No. 2005-35466
Meanwhile, among these brake actuators, there is a brake actuator where a solenoid valve is formed of a valve main body and a coil part in consideration of an assembling property and the like, and the valve main body and the coil part are mounted on a housing and assembled with each other. Specifically, the valve main body includes a valve part and a solenoid part, the valve part is fixed to the housing by inserting the valve part into a mounting hole of the housing, and the solenoid part is arranged so as to be exposed to the outside of the housing. Further, a solenoid is formed by fitting the coil part to the exposed solenoid part so that the coil part surrounds the solenoid part. A spring or the like, which biases the coil part toward the housing, is provided between the terminal box and the coil part. Accordingly, the spring or the like stably supports the coil part by biasing the coil part toward the housing. In this structure, an appropriate gap is formed between the coil part and the solenoid part in consideration of an assembling property of the solenoid valve.
However, through the verification that has been performed in recent years by inventors, it has been found out that backlash caused by the gap becomes a factor causing an abnormal noise and particularly becomes a problem in a very quiet vehicle such as a hybrid vehicle. Meanwhile, it is considered that this problem is not limited to the brake apparatus and likewise rises in an actuator where a coil part and a valve main body as a solenoid valve are separately formed and then are assembled with each other.